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The need to find a balance between risk and cost when remediating contaminated land has led to more research about appropriate levels of specific chemicals.

On January 19, 2017 the United States Environmental Protection Agency (EPA) Integrated Risk Information System (IRIS) program released its final assessment of benzo(a)pyrene (BaP). The final toxicity values from EPA's IRIS have the potential to reduce the need for remediation of BaP and other carcinogenic polycyclic aromatic hydrocarbons (PAHs).

EPA's IRIS program identifies and characterizes the health hazards of chemicals found in the environment. Each IRIS assessment can cover a chemical, a group of related chemicals, or a complex mixture. BaP is released into the atmosphere as a component of smoke from forest fires, industrial processes, vehicle exhaust, cigarettes, and through the burning of fuel (such as wood, coal, and petroleum products).

The EPA has not updated its Regional Screening Levels (RSLs) tables since May 2016, which has effectively delayed the implementation of these toxicity values in site assessments and remediation. However, EPA has updated its RSL calculator, which is used to generate the RSL tables, to incorporate these final toxicity values. The updated BaP RSLs for EPA's default exposure media and scenarios are as follows:

Benzo(a)pyrene RSLs

ExposureMedia and Scenario

Previous RSLs

Updated RSLs

Cancer (TCR = 1E-6)

Noncancer (THQ = 1)

Cancer (TCR = 1E-6)

Noncancer (THQ = 1)

Resident Soil

0.016 mg/kg

NA

0.115 mg/kg

17.8 mg/kg

Industrial Soil

0.29 mg/kg

NA

2.11 mg/kg

222 mg/kg

Resident Air

0.00092 ug/m3

NA

0.00169 ug/m3

0.00209 ug/m3

Industrial Air

0.011 ug/m3

NA

0.0204 ug/m3

0.00876 ug/m3

Tapwater

0.0034 ug/L

NA

0.0251 ug/L

6.02 ug/L

EPA's RSL calculator also includes the final IRIS assessment for Trimethylbenzenes (TMB) from September 9, 2016. EPA's final assessment evaluated the toxicity for the 1,2,3-TMB, 1,2,4-TMB, and 1,3,5-TMB isomers and concluded that all three isomers should use the same toxicity values. The updated TMB RSLs for EPA's default exposure media and scenarios are as follows:

Chemical

Exposure Media and Scenario

Previous RSLs

Noncancer (THQ = 1)

Updated RSLs

Noncancer (THQ = 1)

1,2,3-TMB

Resident Soil

49 mg/kg

336 mg/kg

Industrial Soil

210 mg/kg

2,050 mg/kg

Resident Air

5.2 ug/m3

62.6 ug/m3

Industrial Air

22 ug/m3

263 ug/m3

Tapwater

10 ug/L

55 ug/L

1,2,4-TMB

Resident Soil

58 mg/kg

303 mg/kg

Industrial Soil

240 mg/kg

1,770 mg/kg

Resident Air

7.3 ug/m3

62.6 ug/m3

Industrial Air

31 ug/m3

263 ug/m3

Tapwater

15 ug/L

55.7 ug/L

1,3,5-TMB

Resident Soil

780 mg/kg

271 mg/kg

Industrial Soil

12,000 mg/kg

1,510 mg/kg

Resident Air

NA

62.6 ug/m3

Industrial Air

NA

263 ug/m3

Tapwater

120 ug/L

60.3 ug/L

The RSLs for BaP and the TMBs that use EPA's default exposure factors and updated IRIS toxicity values can be found here.

How can GHD help?

Contact a GHD Risk Assessor for more information. We can help determine the most appropriate path to optimize environmental investigation or cleanup at your site.